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GMC LY6 specs: 364 ci (6.0L) 8-cylinder, 4.00 x 3.622 in (101.6 x 92 mm) bore and stroke. Rated 352-360 hp, 2007–2009. Used in the GMC Sierra HD. OHV.
The GMC 364ci (LY6) is oversquare — the 4" bore exceeds the 3.622" stroke by 10.4% — a layout that favors airflow and RPM over leverage at the crank. The 3.622" stroke puts mean piston speed at 4,000 ft/min around 6,650 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.684 is in the range most production engines fall in. Each of the 8 cylinders displaces 45.5 ci (746 cc).
It is one of 8 engines in the GMC 364ci family, all of them 364 ci — the differences between them are in compression, heads and rating, not displacement. 7 factory variants share these dimensions, rated from 352 to 360 hp across 2007–2009.
| Displacement | 364 ci / 6 L |
|---|---|
| Bore | 4" |
| Stroke | 3.622" |
| Cylinders | 8 |
| Configuration | V8 |
| Rod length | 6.098" |
| Rod ratio | 1.684 |
| Bore/stroke ratio | 1.104 |
| Deck height | 9.24" |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 352–360 hp |
| Years | 2007–2009 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 2009 | LY6 net | 360 @ 5400 * | 380 lb-ft @ 4200 * | — |
Factory specification sheet. * Not yet cross-verified.
| Bore/stroke character | 1.104 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,622 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.684 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 45.5 ci |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 2007 | 352 hp | LY6 |
| 2007 | 353 hp | LY6 |
| 2008 | 352 hp | LY6 |
| 2008 | 353 hp | LY6 |
| 2009 | — | LY6 |
| 2009 | 352 hp | LY6 |
| 2009 | 360 hp | LY6 |
6 factory vehicles, 2007–2009. Each year opens that model's engine table.